1. Technical Field
The present invention relates to a throttle valve for an internal combustion engine. More particularly, this invention relates to a two-part clamshell throttle body which permits a one-piece, drop-in-place method of assembling a throttling member subassembly.
2. Disclosure Information
With advances in plastics technology, the automotive industry continues to push for the use of plastics in place of metal. Aside from weight reduction benefits, plastics are generally more corrosion resistant than many metals. Also, plastic molding techniques minimize complicated machining requirements and reduce the required number of parts so that assembly is simplified and cost is reduced.
The throttle valve is one automotive component which traditionally is composed of many parts. Unfortunately, the high precision relationship of these parts to one another, because of prior art configurations coupled with external environmental factors, has limited their makeup to metallic compositions as opposed to plastics. The use of plastics was not practical due to manufacturing process limitations along with material rigidity and expansion concerns.
Typical throttle valve designs include throttle bodies which are composed of a one-piece housing. This hinders the possibilities of simplifying the throttle valve manufacturing process since the throttle body's internal components (e.g., throttling member subassembly) must be assembled around and into the throttle body on a piece-by-piece basis. Such assembly techniques do not lead to a robust product and often create quality problems since it reduces the opportunities to utilize injection molded plastic technologies which serve to reduce the number of parts.
The present invention resolves this issue by providing a throttle body of a two-piece, clamshell design. With the clamshell, the throttling member subassembly can be constructed independent of the throttle body housing. Once constructed, the throttling member subassembly can then be dropped in place as one part. Without the clamshell design of the present invention, pre-assembly and utilization of injection molded plastics for the throttling member subassembly would be severely limited.
Combustion engine throttle valve art demands that air leakage through the valve be minimal in order to assure that established idle speeds are not erratic. The trend of the automotive industry is directed towards further reducing engine idle speeds. The lower the idle speed, the smaller the idle air flow demand around the throttle valve. Therefore, concerns about air leakage through the throttle valve, in today's market, has become ever more enhanced.
Prior art has minimized air leakage by maintaining a high precision fit between the throttle body bore (walls of the air conduit) and the pivotal throttle plate when in the closed position. To achieve this high precision, prior art has found it necessary to machine bore throttle bodies of cast aluminum and precision stamp throttle plates of a metallic composition. The necessary precision of this arrangement eliminates the opportunity to utilize plastics for the throttle body or the plate.
To further reduce the already low leakage rates, prior art has found it necessary to decrease the plate's closed idle angle position. The reduction of this angle, however, has increased the chances of the metallic plate becoming wedged against the internal cylindrical walls of the metallic throttle body as a result of misalignment or sludge buildup. To further explain, the plate's outer perimeter edge must conform to the internal walls in order to minimize air leakage through the throttle body when the plate is in the closed position. In fact, the tolerance between the plate edge and the wall is often so tight that the plate scrubs or scratches the wall as it pivots to an open position. If the scrubbing is excessive, the plate can become wedged in the closed position. The smaller the plate angle, or degree off-set, at closure, the greater the chances are of excessive scrubbing. Currently, sticking throttle valves, in the closed idle position, is a warranty concern with throttle valve assemblies. With past throttle body designs, a throttle plate with a zero degree off-set at closure was not advisable.
This invention resolves the wedging problems of prior are by utilizing a face sealing ledge. The high precision requirement between the plate's outer perimeter edge and the throttle body internal wall is eliminated because the plate edge no longer requires the surface of the tangentially positioned internal wall to minimize air leakage, but instead utilizes a parallel plane seating arrangement where the plate makes contact with the seat when in the closed position and pivots open, in a perpendicular direction, off of the seat. That is, when the plate pivots open, it lifts perpendicularly off of it's near zero leakage sealing surface instead of scraping along the interior walls of the throttle body.
Relying on the face sealing ledge to create a near zero air leakage rate is superior to relying on the longitudinal surfaces of the internal throttle body walls because it further limits air leakage necessary for today's slower idle speeds, and it eliminates the number one product warranty concern for throttle bodies, that of plate wedging.
French patent 2,606,115 displays a butterfly valve where the shell is divided along the shaft centerline. However, journals and spindles are utilized for end-play limitation and no mention is made of pressed on bearings as taught through this invention. Also, the two shell pieces of the prior art do not incorporate the concepts of a face/ledge seal, zero leakage, or zero plate angle as does the present invention. Instead, the prior art continues with the utilization of an idle stop screw.
German patent 5,687,691 shows a plastic throttling member lever arm which is made of plastic and formed about the end of a metallic shaft utilizing a slot as a means to resist torsion forces. No mention is made of a tang in place of the slot, nor is any mention made of a "slot-free" throttling shaft as taught through the present invention.